"• The number and percentage of persons aged 12 or older who were current nonmedical users of stimulants in 2013 (1.4 million or 0.5 percent) were similar to those in 2012 (1.2 million or 0.5 percent), but were higher than the estimates in 2011 (970,000 or 0.4 percent)."

Source

Substance Abuse and Mental Health Services Administration, Results from the 2013 National Survey on Drug Use and Health: Summary of National Findings, NSDUH Series H-48, HHS Publication No. (SMA) 14-4863. Rockville, MD: Substance Abuse and Mental Health Services Administration, 2014, p. 17.
http://www.samhsa.gov/data/NS…
http://www.samhsa.gov/data/NS…